New to the tax system

Hi, its a bit long I’m afraid but I want to get all the facts in.

We as a family become legally resident in France in Feb 2021 after years of moving between our homes in UK and France at will. We all qualified for 10 year WA Titres de Sejour due to being locked down in France for all of 2020.
The family consists of me (50s), and 2 UK pensioners, my mother (80) and my mother’s brother (83) ie my uncle. My British father died in 2012, in France, and all our French property is still in his name at the tax office and the property tax demands come in his name, and are paid from a joint bank account. The property is in joint names: me, my wife, my mother and my father (decd.)
My wife is now a UK resident and tax resident as she works in London form March 2021 and lives in our flat in London for 90% of the year, only visiting France for holidays. She was unemployed from November 2019 and got to France in time for lockdown. She got a new job in London in March 2021. She gives me an allowance from her taxed earnings for the upkeep of the French property.

We 3 in France need to get in the tax system. We are in the health system.
Last year I set up as an Auto Entrepreneur and filled in the tax questionnaire the tax office sent me. Naively I assumed this would get me in to the tax system. No. But they’re more than happy to take the 23% of my small turn over!

My mother and I have French bank accounts. My uncle doesn’t have a French bank account and getting one is proving difficult and causing problems with Ameli as they will only accept a RIB with FR at the beginning, and in his name. (more on this another day) We all have UK bank accounts.

I am employed as a consultant by my UK Ltd company with a small monthly retainer which isn’t quite enough to pay tax on in UK.
As an Auto Entrepreneur I work for my UK Ltd company providing daily rate services in France for a small number of non French companies, again the income is not large. I make quarterly declarations and payments to URSAAF.

My Mother and Uncle are UK pensioners with income less than £12k each per annum.
I now assume that both my mother and uncle, although low income pensioners have to get a tax number?
I also have to get a tax number and make declarations on the forms in the 2042 series that I found in you FAQ. Yes I know it’s late but I assumed they would send me the forms as I told them I was running a business in France.
I understand that the system works on a household basis.  I look after the finances for both of the pensioners.
Do I make the 2nd declarer my wife (absent in London and paying UK tax) or my mother (UK pensioner?). Or no 2nd declarer and make declarations for her and her brother separately?

Are we likely to be fined for making a late declaration?

How do I get the property taxes moved in to my name from my late father’s?

Nothing regarding his death has been done. I tried contacting some Notaires years ago but none replied.

Lots of questions to start with.
Thanks in advance.
Gruff